Two-stage electrochemical octafluoropropane production

ABSTRACT

1. A PROCESS FOR THE PREPARATION OF OCTANFLUOROPROPANE, WHICH COMPRISES: PASSING AN ELECTRIC CURRENT THROUGH A CURRENT-CONDUCTING LIQUID HYDROGEN FLUORIDE ELECTROLYTE CONTAINED IN A FIRST ELECTROLYSIS CELL PROVIDED WITH A CATHODE AND AN ANODE; PASSING A FIRST FEEDSTOCK COMPRISING PROPANE INTO SAID FIRST ELECTROLYSIS CELL AND INTO CONTACT WITH SAID ANODE AND FLUORINATING SAID FEEDSTOCK IN SAID FIRST ELECTROLYSIS CELL UNDER FIRST FLUORINATING CONDITIONS WHICH FAVOR THE CONVERSION OF SAID FEEDSTOCK TO PERFLUOROPROPANE INTERMEDIATES AS OPPOSED TO THE CONVERSION TO OCTAFLUOROPROPANE; WITHDRAWING FROM SAID FIRST ELECTRLYSIS CELL A FIRST EFFLUENT STREAM COMPRISING UNCOVERTED PROPANE, PERFLUOROPROPANE INTERMEDIATES, AND OCTANFLUOROPROPANE; PASSING THE FIRST EFFLUENT STREAM INTO A FIRST SEPARATION ZONE; WITHDRAWING FROM SAID FIRST SEPARATION ZONE A FIRST OVERHEAD STREAM COMPRISING ALL OF SAID UNCONVERTED PROPANE AND AT LEAST A MAJOR PORTION OF OCTAFLUOROPROPANE, AND A FIRST BOTTOMS STREAM FREE OF PROPANE AND COMPRISING AT LEAST A MAJOR PORTION OF SAID PERFLUOROPROPANE INTERMEDIATES; PASSING AN ELECTRIC CURRENT THROUGH A CURRENT-CONDUCTING LIQUID HYDROGEN FLUORIDE ELECTROLYTE CONTAINED IN A SECOND ELECTROLYSIS CELL PROVIDED WITH A CATHODE AND AND ANODE; PASSING A PROPANE-FREE SECOND FEEDSTOCK COMPRISING AT LEAST A PORTION OF SAID FIRST BOTTOMS STREAM FROM SAID FIRST SEPARATION ZONE INTO SAID SECOND ELECTROLYSIS CELL AND INTO CONTACT WITH THE ANODE OF SAID SECOND ELECTROLYSIS CELL AND FLUORINATING SAID SECOND FEEDSTOCK IN SAID SECOND ELECTROLYSIS CELL UNDER SECOND FLUORINATING CONDITIONS WHICH FAVOR THE CONVERSION OF SAID SECOND FEEDSTOCK TO OCTAFLUOROPROPANE; WITHDRAWING FROM SAID SECOND ELECTROLYSIS CELL A PROPANE-FREE SECOND EFFLUENT STREAM COMPRISING PERFLUOROPROPANE INTERMEDIATES AND OCTAFLUOROPROPANE; PASSING THE SECOND EFFLUENT STREAM TO A SECOND SEPARATION ZONE; WITHDRAWING FROM SAID SECOND SEPARATION ZONE A SECOND OVERHEAD STREAM COMPRISING AT LEAST A MAJOR PORTION OF THE OCTANFLUOROPANE CONTAINED IN SAID SECOND EFFLUENT STREAM AND A PROPANE-FREE SECOND BOTTOMS STREAM COMPRISING AT LEAST A MAJOR PORTION OF THE PERFLUOROPROPANE INTERMEDIATES CONTAINED IN SAID SECOND EFFLUENT STREAM; RETURNING AT LEAST A PORTION OF SAID FIRST OVERHEAD STREAM TO SAID FIRST ELECTROLYSIS CELL TO FORM A PORTION OF SAID FIRST FEEDSTOCK; AND RETURNING AT LEAST A PORTION OF SAID SECOND BOTTOMS STREAM TO SAID SECOND ELECTROLYIS CELL TO FORM A PORTION OF SAID SECOND FEEDSTOCK; WHEREIN SAID FIRST FLUORINATING CONDITIONS COMPRISE REPLACEMENT OF FROM 1 TO 20 PERCENT OF THE REPLACEABLE HYDROGEN OF SAID FIRST FEEDSTOCK WITH FLUORINE, AND TION OF SAID SECOND FLUORINATING CONDITIONS COMPRISE REPLACEMENT OF AT LEAST GREATER THAN 20 PERCENT OF THE REPLACEABLE HYDROGEN OF SAID SECOND FEEDSTOCK WITH FLUORINE.

United States Patent 3,840,445 TWO-STAGE ELECTROCHEMICAL OCTAFLUORO- PROPANE PRODUCTION Robert A. Paul and Murl B. Howard, Bartlesville, Okla.,

assiguors to Phillips Petroleum Company Filed May 15, 1972, Ser. No. 253,006

Int. Cl. C07b 29/06; C07c 17/10, 19/08 US. Cl. 204-59 F 3 Claims ABSTRACT OF THE DISCLOSURE A two-stage electrochemical process comprising: a firststage fluorination wherein propane is fluorinated under regulated conditions in order to produce a maximum amount of partially fluorinated propanes and a minimum amount of octafiuoropropane; a separation step wherein a propane-free stream of partially fluorinated propanes is isolated; and a second-stage fluorination wherein said partially fluorinated propanes are fluorinated under regulated conditions in order to maximize the formation of octafiuoropropane (perfluoropropane).

This invention relates to a process and an apparatus for the preparation of octafiuoropropane (perfluoropropane).

In this application, the phrase partially fluorinated propanes refers to fluorinated propane molecules containing at least one but not more than seven fluoride atoms. The phrase is used interchangeably with octafluoropropane intermediates, perfluoro intermediates, or simply intermediates.

Electrochemical fluorination processes for converting organic compounds into desirable fluorinated compounds are generally known in the art. Recent advances in the state of the art include electrochemical fluorination processes wherein fluorination of organic compounds is carried out within the confines of a porous anode. Such an improved process is capable of producing a broad variety of partially and completely fluorinated products with very little carbon to carbon bond scission which results in undesirable by-products.

In such prior art electrolytic fluorination processes, when charging propane feedstock, there is obtained a mixture of partially and completely fluorinated propanes. There are about 29 such fluoropropanes and most are generally present. In the practice of the prior art processes for the preparation of octafiuoropropane, there is the problem that mixtures of octafiuoropropane and unconverted propane cannot readily be separated. These two materials have similar boiling points and tend to codistill with one another when using conventional fractionation methods. As a result, the conversion of propane to perfluoropropane is complicated because it is difficult to recycle the unconverted propane. Also, it is diflicult to obtain a perfluoropropane product that is not contaminated with significant amounts of propane.

It is an object of this invention to provide an improved electrochemical process for the fluorination of propane to octafiuoropropane. Anther object is to provide an improved electrochemical process which reduces or eliminates separation of octafiuoropropane from mixtures including propane. Another object is to provide a process to regulate or control the fluorination of propane to reduce or eliminate the occurrence of mixtures of propane and octafiuoropropane in the product. Another object is to provide a process for the preparation of mixtures of propane and perfluoropropane intermediates that can be conveniently separated. Still another object is to provide a process for the fluorination of perfluoropropane intermediates to provide mixtures of octafiuoropropane and perfluoropropane intermediates. Still another object is to provide an improved electrochemical process for the continuous fluorination of propane and the recovery of octa- Patented Oct. 8, 1974 fiuoropropane which avoids or substantially reduces the separation of octafiuoropropane from unconverted propane feedstock. Other objects and advantages of this invention will be apparent to those skilled in the art in view of this disclosure and the appended claims.

According to this invention, there is provided a process for electrochemical fluorination of propane feedstock to octafiuoropropane, which process comprises: (a) passing a feedstock comprising propane into a first electrochemical fluorination zone and therein partially fluorinating the propane under conditions suflicient to produce an efiluent stream comprising partially fluorinated propane, unconverted propane, and little or no perfluoropropane; (b) passing said efiluent into a separation zone to produce a first lower boiling mixture comprising propane and perfluoropropane, and a second higher boiling mixture comprising partially fluorinated propane; (c) returning said first mixture to said electrochemical fluorination zone as a portion of said feedstock; and (d) passing said second mixture to a second electrochemical fluorination zone operating under conditions snflicient to produce an eflluent stream comprising a substantially quantity of perfluoropropane.

The advantages realized by operating the first fluorinating zone under conditions to minimize the production of octafiuoropropane combined with operation of the second fluorinating zone under conditions to maximize the production of octafiuoropropane permits the separation, isolation, and recovery of octafiuoropropane conveniently and relatively inexpensively without the necessity for more complex and more costly methods for the separation of mixtures of octafiuoropropane and propane. Thus, in the process of the present invention, mixtures of these difiicultly separable materials are avoided or minimized.

Any suitable electrochemical fluorination process, which is capable of replacing the hydrogen atoms of propane with fluorine atoms, can be used in the fluorination zones of the present invention. However, the presently preferred electrochemical fluorination process comprises passing the propane or the perfluoropropane intermediates feedstock into the pores of a porous anode at a point near the bottom of the porous anode, e.g., porous carbon, immersed in a current-conducting, essentially anhydrous hydrogen fluoride-containing liquid electrolyte such as KF-ZHF. The feedstock contacts the fluorinating species within the pores of the anode and, depending on the conditions, at least some of the hydrogen on the propane or perfluoropropane intermediates are replaced with fluorine. The vaporous fluorinated products leave the pores of the anode at a point above the liquid electrolyte level and exit the cell. Hydrogen is generated at the cathode and, with the aid of a simple cell divider, exits the cell without mingling with the fluorination products. HF is consumed in the process and is continuously or intermittently replaced.

The hydrogen fluoride electrolyte can contain an inorganic additive such as an alkali metal fluoride or ammonium fluoride which desirably reduces the hydrogen fluoride vapor pressure and assists in maintaining adequate conductivity in the electrolyte under the fluorinating conditions employed in this invention. The additives can be employed in any suitable molar ratios of additive to hydrogen fluoride, generally within the range of from 1:45 to 1:1.

Generally speaking, the fluorination process can be carried out at temperatures within the range of from 112 to 932 F. in which the vapor pressure of the electrolyte is not excessive, e.g., less than 250 millimeters Hg. It is preferred to operate at temperatures such that the vapor pressure of the electrolyte is less than about 50 millimeters Hg. Preferred operating temperatures are in the range to 250 F.

Pressures substantially above or below atmospheric can be employed; however, the vapor pressure of the electrolyte must be taken into consideration as discussed hereinbefore. Generally speaking, the process of this invention is carried out conveniently at substantially atmospheric pressure.

Current densities within the range of 30 to 1000 or higher, preferably 50 to 500, amperes per square foot of anode geometric surface, are generally used. Voltage employed will vary depending upon the particular cell configuration as well as the current density desired. Under normal operating conditions, however, the cell voltage or potential will be less than that required to evolve or generate free elemental fluorine. Voltages within the range of 4 to 12 volts are typical. Generally speaking, the maximum normal voltage will not exceed 20 volts per electrolytic cell.

Feed rates which can be employed will preferably be within the range of from 0.5 to 10 milliliters per minute per square centimeter of anode geometric surface area. Since the anode can have a wide variety of geometrical shapes, which will affect the geometrical surface area, sometimes a more useful way of expressing the feed rate is in terms of anode cross-sectional area (taken perpendicular to the direction of flow). Thus, the feed rate can be 3-600 mL/min/cm. of porous anode cross-sectional area. Even more preferably, the feed rate will be such that there is established a pressure balance between the feedstock entering pores of the anode from one direction and the electrolyte attempting to enter the pores from another and opposing direction. Essentially all of the feedstock travels within the porous anode via the pores therein until it exits from the anode at a point above the surface of the electrolyte.

Further details of suitable electrochemical processes can be found in Fox et al. 3,511,760, Childs 3,511,762, application Ser. No. 75,292, filed Sept. 24, 1970, and application Ser. No. 226,039, filed Feb. 14, 1972.

The first electrochemical fluorination zone will operate in a manner essentially identical with that of the second electrochemical zone with two important exceptions. The first is that propane is a feed component to the first zone only; a propane-free stream is fed to the second zone. Thus, the feed stream, including recycle materials, to the first electrochemical fluorination zone is essentially propane and will comprise, including recycle materials, perfiuoropropane, perfiuoropropane intermediates and some hydrogen fluoride. Propane will be absent in the cell and in the recycling and separating stages of the second fiuorination zone. There will, of course, be minor amounts of some heavy and some light products which can be removed from the process at any convenient time andv location.

The second important condition which is different between the two fluorination zones is the degree of conversion of replaceable hydrogen on the feedstock molecules. In the first electrocehmical fluorination zone the electrical current and organic flow rates are such that only 1-20%, preferably l5%, of the replaceable hydrogens are converted. Since two Faradays are required to convert one hydrogen equivalent, this means that only about 2-40 Faradays are passed through the cell with the simultaneous passage of 100 hydrogen equivalents. Such a condition has the effect of maximizing the conversion of propane to intermediates yet minimizes the conversion of propane to perfiuoropropane.

In the second electrochemical fluorination zone, the current and flow rate of organic feedstock are proportioned to provide a replaceable hydrogen conversion of 2190%, preferably 2550%. Such conditions have the effect of maximizing the efiicient conversion of lower fiuorinated intermediates to higher'fiuorinated intermediates and to perfiuoropropane, with minimum losses to cracked or heavy products.

Other conditions can also differ between the two fiuorination zonesbut these are less important and not critical in obtaining the advantage of the invention. For example, it can be advantageous to maintain a somewhat lower temperature in the first zone, e.g., 160-220 F., than the temperature of the second zone, e.g., l250 F. Similarly, somewhat lower current densities, e.g., 50200 amp/ft. can be advantageous in the first fluorination zone as compared with 500 amp/ft. in the second zone. Also, to minimize per-fluorination of propane in the first fluorination zone, it can sometimes be advantageous to maintain a relatively high organic flow rate, with respect to the cross-sectional area of the porous anode, to provide, in turn, a relatively high linear velocity through the anode.

Thus, elongated anodes with relatively thin sections of porous carbon through which the vaporous feed migrates are sometimes advantageous in the firstfiuorination zone. This is less important in the second fluorination zone.

Referring now to the drawing, the sole figure is a simplified diagrammatic representation of the apparatus and process of the present invention. In the figure, there are represented, in combination, cell zone 10, separation zone 20, cell zone 30, and separation zone 40. Cell zone 10 and 30 each represent one or more cells which can be connected in series or parallel and which are suitable for electrochemical fluorination. Each cell in cell zone 10 contains a porous carbon anode 11, a cathode 12, a cell divider 13 which separates the vapor space of the cell into a cathode space and anode space, an HF-containing and current-conducting electrolyte 14, and a hydrogen exit 15. Similarly, each cell in cell zone 30 contains a porous carbon anode 31, a cathode 32, a cell divider 33, an HF-containing electrolyte 34, and a hydrogen exit 35. Separation zones 20 and 40 each comprise one or more suitable fractionation means such as one or more fractionators, including suitable heaters, condensers, packed columns or the like, to effect the desired separations hereinafter described.

In operation, propane feed in line 1 is mixed with recycle materials from line 5 and passed into cell zone 10 through line 2. The feedstock in line 2 passes into the bottom of each porous carbon anode 11 of cell zone 10 and travels upward through anode 11, being fiuorinated during this passage. The fiuorinated products exit anode 11 into the vapor space defined by cell divider 13, and then exit the cell zone through line 3. Hydrogen exits the cell zone through line 15.

The fiuorinated mixture in line 3, comprising perfiuoropropane, intermediates, uncoverted propane, and some hydrogen fluoride is conducted to separation zone 20. Perfiuoropropane, unconverted propane, and some hydrogen fluoride are removed from separation zone 20 as a lower boiling overhead stream and are recycled back to cell zone 10 through lines 5 and 2. Depending on the operation of the separation zone, a small amount of intermediates can also be present in line 5. A portion, about 1-20 wt. percent, of the flow in line 5 can be removed from the process by line 4, if desired, to prevent build-up of perfiuoropropane.

An essentially propane-free stream comprising intermediates and some hydrogen fluoride is passed from separation zone 20 as a higher boiling bottom stream into cell zone 30 via lines 6 and 7. Further fiuorinated materials are passed from cell zone 30 through line 8 into separation zone 40. A small amount of light (cracked) materials exit separation zone 40 through line 18 and a small amount of heavy products exit through line 19. Essentially propanefree perfiuoropropane is obtained as the principal product through line 9. Intermediates leave separation zone 40 and are recycled to cell zone 30 through lines 17 and 7. Hydrogen fluoride feed is passed, as required, into cell zone 10 and cell zone 30 through line 16.

If desired, separation zones 20- and 40 can comprise means, such as caustic or bauxite aborbers, to remove hydrogen fluoride from the various streams. However,

except for the stream of the perfluoropropane product, this is not ordinarily considered to be necessary.

ILLUSTRATIVE EXAMPLE Propane is electrochemically converted to octafluoropropane using the apparatus and the sequence of steps as generally outlined in FIG. 1. Cell zone comprises a battery of cells containing a total of 42.88 ft. of porous carbon anode surface. The anodes are in the form of cylinders of porous carbon which are vertically immersed, almost completely, in the electrolyte. The cylinders are composed of a porous carbon having a total porosity of 51% and whose average pore size is 55 microns. Each cylinder contains a cavity at its bottom into which the gaseous feed is introduced. The feed diffuses upward through the porous carbon anode and exits the anode at a point above the liquid electrolyte level. An iron screen cathode surrounds each anode and each cell has a domed divider (skirt) which separates the vapor space of each cell into a cathode chamber, from which the cathodicallygenerated hydrogen gas is removed, and an anode chamber, from which the anodically-generated product vapors are removed. The electrolyte is KF, and HF is continuously added at a rate sufiicient to maintain a molten composition similar to KF-ZI-IF. Other operating conditions include a current density of 100 amp/ft. of anode surface, a current level of 4288 amps, a temperature of 180 F., atmospheric pressure, and a feed rate suflicient to convert 10% of the replaceable hydrogen in the feedstock.

Cell zone 30 is essentially identical to cell zone 10 we cept that it contains 32.16 ft. of porous carbon anode surface. It is operated at 200 amp/ft? of anode surface, at a current level of 6432 amps, at atmospheric pressure, at a temperature of 205 F., with a molten KF-2HF electrolyte, and at a feed rate suflicient to convert 30% of the replaceable hydrogen.

Exemplary simplified flow rates and stream compositions associated with the process are shown in Table I Norm-(1) Some HF is carried out of cell zone 10 through line 3 and most of this is carried into cell zone 30 through lines 6 and l. (2) Some HF is similarly carried out of cell zone 30 through hne 8 and 18 returned to cell zone 30 through lines 7 and 17.

This example shows a process which utilizes a combination of two electrochemical fluorination zones to conveniently convert propane to octafluoropropane without the necessity of making the difiicult separation of octafluoropropane from propane.

We claim: 1. A process for the preparation of octafluoropropane, which comprises:

passing an electric current through a current-conducting liquid hydrogen fluoride electrolyte contained in a first electrolysis cell provided with a cathode and an anode;

passing a first feedstock comprising propane nto said first electrolysis cell and into contact with said anode and fluorinating said feedstock in said first electrolysis cell under first fluorinating conditions which favor the conversion of said feedstock to perfluoropropane intermediates as opposed to the conversion to octafluoropropane;

withdrawing from said first electrolysis cell a first eflluent stream comprising unconverted propane, perfluoropropane intermediates, and octafluoropropane; passing the first eflluent stream into a first separation zone;

withdrawing from said first separation zone a first overhead stream comprising all of said unconverted propane and at least a major portion of octafluoropropane, and a first bottoms stream free of propane and comprising at least a major portion of said perfluoropropane intermediates;

passing an electric current through a current-conducting liquid hydrogen fluoride electrolyte contained in a second electrolysis cell provided with a cathode and an anode; passing a propane-free second feedstock comprising at least a portion of said first bottoms stream from said first separation zone into said second electrolysis cell and into contact with the anode of said second electrolysis cell and fluorinating said second feedstock in said second electrolysis cell under second fluorinating conditions which favor the conversion of said second feedstock to octafluoropropane;

withdrawing from said second electrolysis cell a propane-free second efiluent stream comprising perfiuoropropane intermediates and octafluoropropane;

passing the second effluent stream to a second separation zone;

withdrawing from said second separation zone a second overhead stream comprising at least a major portion of the octafiuoropropane contained in said second effluent stream, and a propane-free second bottoms stream comprising at least a major portion of the perfluoropropane intermediates contained in said second eflluent stream;

returning at least a portion of said first overhead stream to said first electrolysis cell to form a portion of said first feedstock; and

returning at least a portion of said second bottoms stream to said second electrolysis cell to form a portion of said second feedstock;

wherein said first fluorinating conditions comprise replacement of from 1 to 20 percent of the replaceable hydrogen of said first feedstock with fluorine, and wherein said second fluorinating conditions comprise replacement of at least greater than 20 percent of the replaceable hydrogen of said second feedstock with fluorine.

2. A process in accord with claim 1 wherein said first fluorinating conditions comprise simultaneously passing proportionately from about 2 to 40 Faradays for each hydrogen equivalents passing through said first electrolysis cell, and wherein said second fluorinating conditions comprise simultaneously passing proportionately at least greater than 40 Faradays for each 100 hydrogen equivalents passing through said second electrolysis cell.

3. A process in accord with claim 2 wherein said first fluorinating conditions comprise a first cell temperature within a range of from about F. to about 220 F., and a first cell current density of from about 50 to about 200 amperes per square foot of anode surface, and wherein said second fluorinating conditions comprise a second cell temperature within a range of from about F. to about 250 F., and a second cell current density of from about 100 to about 500 amperes per square foot of anode surface.

References Cited UNITED STATES PATENTS 3,650,917 3/1972 Ruehlen 204-59 R 3,660,254 5/1972 Dunn 20459 R 3,709,800 1/1973 FOX 20459 R 3,645,863 2/1972 Stewart 204-59 R FREDERICK C. EDMUNDSON, Primary Examiner U.S. Cl. X.R. 20472 

1. A PROCESS FOR THE PREPARATION OF OCTANFLUOROPROPANE, WHICH COMPRISES: PASSING AN ELECTRIC CURRENT THROUGH A CURRENT-CONDUCTING LIQUID HYDROGEN FLUORIDE ELECTROLYTE CONTAINED IN A FIRST ELECTROLYSIS CELL PROVIDED WITH A CATHODE AND AN ANODE; PASSING A FIRST FEEDSTOCK COMPRISING PROPANE INTO SAID FIRST ELECTROLYSIS CELL AND INTO CONTACT WITH SAID ANODE AND FLUORINATING SAID FEEDSTOCK IN SAID FIRST ELECTROLYSIS CELL UNDER FIRST FLUORINATING CONDITIONS WHICH FAVOR THE CONVERSION OF SAID FEEDSTOCK TO PERFLUOROPROPANE INTERMEDIATES AS OPPOSED TO THE CONVERSION TO OCTAFLUOROPROPANE; WITHDRAWING FROM SAID FIRST ELECTRLYSIS CELL A FIRST EFFLUENT STREAM COMPRISING UNCOVERTED PROPANE, PERFLUOROPROPANE INTERMEDIATES, AND OCTANFLUOROPROPANE; PASSING THE FIRST EFFLUENT STREAM INTO A FIRST SEPARATION ZONE; WITHDRAWING FROM SAID FIRST SEPARATION ZONE A FIRST OVERHEAD STREAM COMPRISING ALL OF SAID UNCONVERTED PROPANE AND AT LEAST A MAJOR PORTION OF OCTAFLUOROPROPANE, AND A FIRST BOTTOMS STREAM FREE OF PROPANE AND COMPRISING AT LEAST A MAJOR PORTION OF SAID PERFLUOROPROPANE INTERMEDIATES; PASSING AN ELECTRIC CURRENT THROUGH A CURRENT-CONDUCTING LIQUID HYDROGEN FLUORIDE ELECTROLYTE CONTAINED IN A SECOND ELECTROLYSIS CELL PROVIDED WITH A CATHODE AND AND ANODE; PASSING A PROPANE-FREE SECOND FEEDSTOCK COMPRISING AT LEAST A PORTION OF SAID FIRST BOTTOMS STREAM FROM SAID FIRST SEPARATION ZONE INTO SAID SECOND ELECTROLYSIS CELL AND INTO CONTACT WITH THE ANODE OF SAID SECOND ELECTROLYSIS CELL AND FLUORINATING SAID SECOND FEEDSTOCK IN SAID SECOND ELECTROLYSIS CELL UNDER SECOND FLUORINATING CONDITIONS WHICH FAVOR THE CONVERSION OF SAID SECOND FEEDSTOCK TO OCTAFLUOROPROPANE; WITHDRAWING FROM SAID SECOND ELECTROLYSIS CELL A PROPANE-FREE SECOND EFFLUENT STREAM COMPRISING PERFLUOROPROPANE INTERMEDIATES AND OCTAFLUOROPROPANE; PASSING THE SECOND EFFLUENT STREAM TO A SECOND SEPARATION ZONE; WITHDRAWING FROM SAID SECOND SEPARATION ZONE A SECOND OVERHEAD STREAM COMPRISING AT LEAST A MAJOR PORTION OF THE OCTANFLUOROPANE CONTAINED IN SAID SECOND EFFLUENT STREAM AND A PROPANE-FREE SECOND BOTTOMS STREAM COMPRISING AT LEAST A MAJOR PORTION OF THE PERFLUOROPROPANE INTERMEDIATES CONTAINED IN SAID SECOND EFFLUENT STREAM; RETURNING AT LEAST A PORTION OF SAID FIRST OVERHEAD STREAM TO SAID FIRST ELECTROLYSIS CELL TO FORM A PORTION OF SAID FIRST FEEDSTOCK; AND RETURNING AT LEAST A PORTION OF SAID SECOND BOTTOMS STREAM TO SAID SECOND ELECTROLYIS CELL TO FORM A PORTION OF SAID SECOND FEEDSTOCK; WHEREIN SAID FIRST FLUORINATING CONDITIONS COMPRISE REPLACEMENT OF FROM 1 TO 20 PERCENT OF THE REPLACEABLE HYDROGEN OF SAID FIRST FEEDSTOCK WITH FLUORINE, AND TION OF SAID SECOND FLUORINATING CONDITIONS COMPRISE REPLACEMENT OF AT LEAST GREATER THAN 20 PERCENT OF THE REPLACEABLE HYDROGEN OF SAID SECOND FEEDSTOCK WITH FLUORINE. 